(1) Field of the Invention
The present invention relates to molten metal containment systems and structures used, for example, for conveying molten metal from one location to is another, e.g. from a metal melting furnace to a metal casting mold or casting table. More particularly, the invention relates to such structures containing a refractory (usually ceramic) vessel, e.g. a metal distribution trough, crucible, or the like, contained within an outer metal casing used to support, protect and locate the refractory vessel.
(2) Description of the Related Art
Metal containment structures of this kind suffer from the disadvantage that the refractory vessel may become extremely hot during use due to contact with the molten metal (e.g. 680° C. to 750° C. when conveying molten aluminum or aluminum alloys). If this heat is transferred to the outer metal casing of the structure, the metal casing may be subjected to expansion, warping or distortion which, in turn, may cause cracks to form in the vessel or, if the refractory vessel is made in sections, may cause gaps to form between the sections, thereby allowing molten metal to leak from the vessel into the casing. Additionally, the outer surfaces of the casing may assume an operating temperature that is unsafe for operators of the equipment. These disadvantages are made worse if additional heating is applied to the exterior of the vessel within the casing to maintain the molten metal at a desired high temperature. For example, temperatures of up to 900° C. may be reached on the outside of the vessel when further heating of this kind is employed. Layers of insulating material may be provided between the vessel and the interior of the casing, but such layers may not be sufficient to maintain an acceptable temperature at the outer surface of the casing without unduly increasing the width of the walls of the metal containment structure.
It may also be possible to form an air gap within the casing to provide further thermal isolation from the vessel. For example, U.S. Pat. No. 5,316,071, which issued to Skinner et al. on May 31, 1994, discloses a molten metal distribution launder having an air gap or air gaps between layers of insulation and an outer metal casing or shell. A blower is employed to move air longitudinally along the side wall cavities to cool the support structure. However, the provision of such an arrangement of blowers is complex and expensive, and therefore undesirable.
There is, accordingly, a need for improved means of providing support for a refractory metal containment vessel, such as a trough, within a metal casing of a metal containment structure while avoiding unduly elevated temperatures at the outer casing surfaces.